Special features of subarachnoid hemorrhage of unknown origin: a review of a series of 179 cases.

Objectives: The aim of this study was to work out the special features of subarachnoid hemorrhage (SAH) of unknown origin in respect of diagnostic evaluation, clinical course, and outcome in a large cohort of patients.

Methods: We reviewed the data of 179 patients with SAH of unknown origin during 1991 and 2008. The differentiation between perimesencephalic (PM-SAH) and non-perimesencephalic SAH (NON-PM-SAH) was done under consideration of the bleeding pattern on CT scanning.

Results: Among 1226 treated patients with spontaneous SAH over a time period of 17 years, a bleeding source remained undetected on first digital subtraction angiogram (DSA) in 179 patients (16.7%)--47 PM-SAH (26.3%) and 132 NON-PM-SAH (73.7%). The clinical signs of patients with PM-SAH were less marked compared to those with NON-PM-SAH, equally to the Hunt and Hess grade. magnetic resonance imaging (MRI) and MR angiography had 100% negative findings for non-aneurismal bleeding sources in all patients. Second DSA revealed a bleeding source in the NON-PM group in 10.8%. The clinical course of the patients with NON-PM-SAH showed a significantly higher rate of complications and a mortality of about 10%. The outcome was excellent in the PM group, in contrast to a fatal course in 13 cases in the NON-PM group.

Discussion: PM-SAH imposed with a mild clinical course and an excellent outcome, without severe complications. In contrast to this, NON-PM-SAH has a significant higher rate of dreaded complications and mortality. It is crucial to make an exact diagnosis of PM-SAH, considering CT scanning during the first 24 hours after occurrence of symptoms and the radiological features.